1. Field of the Invention
The invention relates to an apparatus and a method in each case for treating slurries, particularly of industrial or biogenic origin.
2. Background and Relevant Art
Such apparatuses and methods are used for the treatment or even renovation of slurries, particularly of slurries of industrial origin, slurries from mining operations, sedimentary slurries in bodies of water and/or biogenic slurries.
Biogenic slurries of animal or human origin are usually mixtures of a liquid phase or liquid, mostly mainly water, and a solid phase or solid particles. The solid phase in this case usually comprises biogenic particles or organic solids, cells and microorganisms, in particular bacteria, and aggregates of these. In addition, biogenic slurries may comprise organic or inorganic substances and also a gas phase, for example in the form of gas bubbles or dissolved gas. The gas may come from the aerobic or anaerobic decomposition of organic material. Biogenic slurries from waste water purification are also designated sewage slurries.
In sewage plants, the waste water or dirty water to be purified usually comes, after mechanical prepurification, into a detritus pit in which un-dissolved substances, such as faecal substances and paper, etc., settle or float on the surface. Pretreated dirty water is then usually subjected to a biological clarifying stage. In this case, organic substances are decomposed, in particular, aerobically by microorganisms and inorganic substances are partially oxidized. Customary methods for this biological stage are activated sludge methods with subsequent secondary clarification. In the activated sludge method, biogenic contents of the waste water or dirty water are continuously decomposed, with the supply of air, biotically by oxidation and aerobically by the addition of activated sludge which contains bacteria aggregated, for example, in flaky form. During secondary clarification, the activated sludge settles and is thus separated from the waste water. Part of the sludge can be recirculated as what is known as return sludge into the activated sludge method in order to keep the concentration of microorganisms sufficiently high. The excess sludge which has occurred due to the growth of biomass during secondary clarification is thickened, for further treatment, together with the primary sludge from preclarification and is then decomposed further anaerobically, for example, in digestion towers. Digested sludge resulting from this, after passing through a secondary thickener, is delivered to a sludge press for dewatering and, after being dewatered, can be disposed of. Clarification methods may also be carried out without preclarification. In this case, only the excess sludge from secondary clarification is delivered to the sludge press via a prethickener, usually without a digestion tower.
For the dewatering of slurries, in particular sewage or industrial slurries or sedimentary slurries, it is known to separate the slurry liquid fraction, composed essentially of water, by means of a filter plant or centrifuge, solid constituents simultaneously being separated from the slurry. Furthermore, dewatering with bags or hoses made from (geo) textile filter materials is also known.
A flocculent (a flocking aid) which contains polymers is usually mixed with the slurry before dewatering, in order to increase the degree of dewatering or degree of drying of the slurry, that is to say to dewater the slurry more effectively. The way in which the flocculent acts may be imagined as being that the polymers bind the solid particles in the slurry to one another in flakes or so as to form flakes and thereby assist or improve their separation from the water. The dewatered dry mass filtered out is also designated as a filter cake. The polymers also improve the passage of water through the filter cake in the case of the subsequent slurry quantities.
DE 198 08 156 A1 discloses an apparatus for the treatment of conditioning agent (flocculent) for aqueous slurry, with a rotating distributor head for mixing a mixture of active substance parent solution and additional water in a mixing chamber and with an inoculating device which dispenses the active substance solution mixed in the mixing chamber, as conditioning agent, to the aqueous slurry flowing in a feed pipe. The distributor head has, distributed about its axis of rotation, essentially two longitudinal slots running parallel to the axis of rotation, as fluid outlets for the mixture, and also two mixing blades extending radially outward and along the axis of rotation and designed as strips. The longitudinal slots are arranged in the circumferential direction between the mixing blades. The mixture flows through a shank of the distributor head and through the slot shaped fluid outlets outward into the mixing chamber and is fully mixed there by the two mixing blades. The mixing blades have on their outer circumference or region located radially furthest outward, in a first embodiment, mixing-in edges running parallel to the axis of rotation and end edges adjoining these axially at the front and rear and running inward in a curved manner or, in a second embodiment, circular mixing-in edges running in a longitudinal plane containing the axis of rotation. The mixing in edges of the mixing blades swirl and mix the flocculent, introduced via the slots, in the slurry. The rotational speed of the distributor head is set in a range of between 700 rev/min (revolutions per minute) and 2500 rev/min.
The effectiveness of the biological purification stage in sewage plants can be increased in that homogenizers or else disintegrators are used for treating the sewage sludge, in particular the return sludge, primary sludge or excess sludge and also digested sludge.
By means of such disintegrators, the size of the solid particles contained in the sludge can be reduced and homogenized, with the result that a larger effective surface for decomposition becomes available. Furthermore, by disintegration, enzymes adhering to cell walls and biogenic particles can be detached and thus introduced into the liquid phase. Further, in disintegration, cell walls of cells and the like can be at least partially broken up, with the result that endoenzymes of the cells are released. In particular, the disintegration actions mentioned increase the efficiency of biological decomposition by microorganisms in the sludge, in particular in the activated sludge of the biological decomposition stage.
A disintegration rotor for sewage sludges is known, for example, from DE 37 19 441 A1. The known disintegration rotor has twisted blades with a curved front. Rotation of the disintegration rotor in the sludge results in disintegrating cavitation effects.
A disintegration rotor having external blades for sewage sludges is known from JP-2002 248493. When this disintegration rotor rotates, disintegration is brought about by cavitation between the blades.
U.S. Pat. No. 6,402,065 B1 discloses a disintegration rotor with blades arranged parallel to the axis of rotation, in which rotor the sludge flows radially.
DE 20 2005 000 875 U1 discloses a disintegration rotor in which the sludge is routed radially from the inside outward through partially nozzle like cavities.
Disintegration of sludges can admittedly be achieved by means of the known disintegration rotors. However, the achievable disintegration action is still worth improving.